Speaking at the University of Exeter the Prime Minister told an audience of students they had the most to gain and the most to lose. He told them: “talk to your parents and grandparents and say this is a vote for your futures.”

He added: “this is probably the most important political decision of your lifetime”, urging them “whatever you do, turn up and vote”.

David Cameron will be well aware of the opinion poll results indicating that voters aged 55 and over are not only much more likely to be eurosceptic than the young, but are also much more likely to actually go out and cast a vote.

Research by the Electoral Commission shows that only 76 per cent of 18-19 year olds and 70 per cent of 20-24 year olds are registered to vote.

To take part in the EU referendum on 23 June, would-be voters need to register by 7 June.I don't know if I'm registered - what should I do?Check with your local electoral registration office: you can find the details here.I need to register to vote - can I do it online?Yes, it should take around five minutes. Register here.

“Propaganda”

Mr Cameron also defended the decision to spend nine million pounds of taxpayers’ money to send each household a leaflet setting out the case for staying in the EU.

The leaflet was denounced by the Justice Secretary Michael Gove, who is campaigning to leave the EU. He told the BBC: “I just think it is wrong that at a time of austerity, £9m of taxpayers’ money is being spent on a one-sided piece of propaganda.

That money should be being spent on the NHS and the people’s priorities.”

But the Prime Minister insisted the government publication was not undemocratic, saying “We are not neutral so we have made a clear stance in this leaflet which everyone will get a copy of.”